The present invention relates to a method for determining an electrical torque of an electrical machine, wherein the method includes a first step of determining an electrical torque in a first speed range with a first algorithm.
The invention further relates to an apparatus for determining an electrical torque of an electrical machine.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
In the case of variable-speed electrical three-phase drives for industry (for example in production machines, machine tools and electric vehicles), safety technology is used to protect people and machines by implementing, for example, functions such as “safely limited speed”, “safe stop” and “safe operation stop.” These functions in accordance with the prior art are not sufficient to cope with all hazard situations.
This is explained using the following example: a machine component consists of driven rollers (similar to a mangle). The material is transported or processed via the rollers. For maintenance purposes, repair purposes and cleaning or for removing trapped material the operator has to reach into the machine component. It is also necessary for the rollers to move for the maintenance, repair or cleaning operation. To this end the rollers are operated at ‘safely reduced speed’. However, despite the reduced speed a potential hazard still exists. If for example a finger is caught between the rollers, it is injured. Or the person is no longer able to move away from the machine component in the event of danger. Other examples are window raising systems in cars or elevator doors.
Hence in addition to safely limiting the speed, a way of safely limiting the torque is required. The torque should be limited sufficiently so that when a finger gets between the rollers, the maximum torque generated by the rollers is such that there is still no risk of injury or that the counter-torque of the finger brings the rollers to a standstill. This “safe torque limiting” function, known as ‘Safely Limited Torque’ (SLT), now forms part of IEC61800-5-2 (CD).
In the case of electric vehicles, no dangerous situation should likewise occur in the event of an error. In electric vehicles the drive is given a desired torque value (with a gas pedal). The actual torque of the drive may differ only slightly from the desired value, or at least may exceed the desired value only very slightly, as in the event of larger deviations the vehicle can, under certain circumstances, no longer be controlled. Hence reliable detection of the torque with appropriate monitoring is necessary. In the prior art clutches, slip clutches, rupture joints or torque sensors are used for this.
It would therefore be desirable and advantageous to obviate prior art shortcomings and to provide an improved method and an apparatus with which an electrical torque of an electrical machine can be determined more accurately over a wide range of speeds.